Pendulum light sensor

ABSTRACT

A pendulum light sensor mounted on the cutting tool of a surface finishing machine for automatically adjusting the angle of the cutting tool upon the raising and lowering of same to effect a deeper or shallower cut; said sensor incorporating a liquid chamber within which is disposed a bubble housing having a switch control arm attached thereto for opening and closing a photoelectric cell switch within the housing upon rotatable movement of said cutting tool. The photoelectric cell switch is in circuit with an elevator mechanism for raising and lowering the cutting tool to maintain the angle of the cutting tool at a predetermined attitude above the ground surface at all times.

United States Patent 1 1 i t al. 1 51 Dec. 4, 1973 PENDULUM LIGHT SENSOR 2,958,786 11/1960 Millis 250 231 3,097,565 7 1963 Kupelian... 33 366 x [75] Inventors- Raymond g 3,354,320 11 1967 Dryden 250/231 McMahm, both 0f Peoria 3,377,714 4/1968 Carlson 33/396 73 1 z 3,400,579 9/1968 Parmater et a1. 250 231 Asslgnee 322 22 3? Brake Company 3,564,531 2/1971 Bargin 1. 172 45 x 3,597,090 8/1971 Humphrey 356/250 22 Fil d; 1971 3,657,551 4 4/1972 Lingert et a1. 250 231 [21] Appl. No.: 209,327

Primary Examiner-Stephen C. Pellegrino Att0rneyRobert J. Eek

[57] ABSTRACT A pendulum light sensor mounted! on the cutting tool of a surface finishing machine for automatically adjusting the angle of the cutting tool upon the raising and lowering of same to effect a deeper or shallower cut; said sensor incorporating a liquid chamber within which is disposed a bubble housing having a switch control arm attached thereto for opening and closing a photoelectric cell switch within the housing upon rotatable movement of said cutting tool. The photoelectric cell switch is in circuit with an elevator mechanism for raising and lowering the cutting tool to maintain the angle of the cutting tool at a predetermined attitude above the ground surface at all times.

13 Claims, 5 Drawing Figures Z) 23 Z3, g z; Z0 E 25 X4 22:- l 22 I 0 22 /O' k ii 1 iv/n l 26 2Q l l 1, 6 a x TA J PATENTEU DEC 4 I975 3.776315 SHEET? 0F 2 PENDULUM LIGHT SENSOR The present invention relates in general to surface finishing equipment and more particularly, to a pendulum light sensor for automatically adjusting the angle of a cutting tool therefor.

Heretofore, the prior art surface finishing equipment employed pendulum weights for sensing deviations from the horizon. Such weights were in operative engagement with hydraulic valves, electro micro switches, linear variable differential transformers, electric potentiometers, and the like, to produce a signal for actuating electric solenoid valves, which in turn ad justed the cutting edge of the blade to the correct position as noted by the pendulum deviation. All of the prior art pendulum sensors required work output either at the. switch or at the signal producer thereby requiring a most sensitive instrument since the friction and other forces acting thereon would result in inefficient operation. Therefore, such prior art apparatuses were necessarily extremely delicate, costly in manufacture and required extensive care and maintenance.

By the present invention, the above disadvantages have been alleviated by using a pendulum light sensor incorporating an incapsulated air bubble whice floats within a liquid chamber having a flag arm attached thereto which is positioned between photoelectric cells connected in circuit with an electrohydraulic valve. The flag arm is interposed between light projecting means and the photoelectric cells so that circuit is closed upon swingable movement of the flag arm thereby requiring virtually no friction or resistance during movement of the flag arm. Since the apparatus of the present invention has few moving parts a simple maintenance is achieved while being economical in manufacture and durable in usage. Said pendulum light sensor may be utilized over relatively long periods of time without adjustment while being capable of precision adjustment within 0.005 inch. Moreover, the flag arm of the present invention is adjustable so that different tolerances may be readily obtained depending upon the particular specifications of the job. Importantly, the position sensing apparatus of the present invention is a relatively simple construction and may be easily incorporated within existing surface finishing equipment so as to avoid costly modification and installation.

The liquid level within the apparatus may also be adjusted to float the incapsulated bubble with the greatest liquid displacement thereby creating a force to cancel the friction at the pivot point thereof. Thus, the apparatus of the present invention performs with a minimum of friction thereby enhancing its sensitivity as the work done by the bubble and the flag arm is such that they move relatively without friction between the light switches and with the pivot point of friction being cancelled by the bubble force action.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical transverse section taken through a surface finishing vehicle illustrating a pendulum light sensor constructed in accordance with and embodying the present invention.

FIG. 2 is a front elevational view.

FIG. 3 is a vertical section taken on the line 3--3 of FIG. 2.

FIG. 4 is a horizontal section taken substantially on the line 4-4 of FIG. 2.

FIG. 5 is an electro-hydraulic shcematic diagram.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings wherein like reference characters designate like corresponding parts, there is shown in FIG. 1 a surface finishing vehicle 20, such as a grader or the like, comprising a frame 21 which is supported above ground in the customary fashion by a plurality of wheels 22. Fixed to the forward portion of the frame 21 on each side thereof is an elevator mechanism E,E', such as the customary lift device 23,23, respectively, each being operatively engaged to a hydraulic ram 24,24, respectively, having an extensible and retractable piston 25,25, of the double-acting type, fixed at its outer end portion to the draw bar 26. Mounted to the underside of draw bar 26 is the conventional circle 27 having fixed thereto, in diametrically opposed portions, an arcuate support leg 28,28, which in turn is connected to the mold board 29 having an elongate cutting blade 30 secured thereto. Although the hydraulic rams 24,24 constitute the preferred embodiment of the present invention for raising and lowering the cutting blade 30 to the associated structure, it will be understood that a hydraulic motor and worm gear system may be readily substituted for the hydraulic ram 24,24 to raise and lower the blade 30 by rotation.

Fixed to the rearward face of the mold board 29, there is a pendulum light sensor A having a verticle axis vv coextensive with the transverse axis of the cutting blade; a horizontal axis h-h in parallel relationship with the longitudinal axis of the cutting blade 30; and a depth axis zz (FIG. 3) in parrallel relationship to the path of travel of vehicle 20. The pendulum light sensor A is presented at the desired angle through a cable c which extends upwardly for suitable attachment to a hand crank control C located in the region adjacent the steering wheel s of the vehicle 20. As will be further described hereinbelow, the pendulum light sen sor A is connected in circuit with said hydraulic ram 24 for efiecting the raising and lowering of the piston 25 to adjust the slope angle of the cutting blade 30. The other hydraulic ram 24 is connected in circuit with a position sensing apparatus (not shown) which is adapted to ride along the customary reference string (not shown) as is shown and described in detail in my co-pending application entitled POSITION SENSING APPARATUS, Ser. No. 160,741, filed July 8, 1971.

For purposes of description, the terms upwardly and downwardly will denote direction relative to the vertical axis v-v of the pendulum light sensor A; the terms inwardly and outwardly will denote direction relative to the horizontal axis hh thereof; and the terms forwardly" and rearwardly' will denote direction relative to the depth axis z-z (FIG. 3).

Said pendulum light sensor A comprises a body 31 of the forward and rearward walls 32,33. Each interior face 36,36 incorporates a peripheral end wall 37,37 respectively, which is received within an annular recess 38,38, respectively, machined within the inner face 39 of said side wall 34 in the region immediately adjacent said forward and rearward walls 32 and 33. Each end wall 37,37 of the respective interior face 36,36 is formed with a peripheral notch 40,40, which accommodates a sealing gasket 41,41, respectively, such as an O-ring or the like, to seal the adjoining peripheral margins between the inner face 39 of said sidewall 34 and the related interior face 36,36. As best observed in FIG. 3, the inner face 39 of side wall 34 and the opposed interior faces 36,36 cooperate to define a chamber 42.

Received within the chamber 42 is a U-shaped support frame 43 having a pair of spaced-apart flanges 44,44 presented in flatwise, but slideable, engagement within guideways g,g machined in the associated interior face 36,36, and joined at their lower end portions by a web 45 spacedly from the inner face 39. The upper, or web-remote, end portions of each flange 44,44 is formed with an elongate, horizontally disposed slot 46,46, respectively, within which is received the related end portion s of a bar 47. The vertical dimention of the bar 47 is substantially the same as that of said slots 46,46, while the horizontal dimention of the bar 47 is slightly less than that of said slots 46,46 for permitting restricted lateral movement. Intermediate the flanges 44,44, said bar 47 is tapped with an opening 48 for threadedly receiving the shank 49 of an adjustment screw 50 which projects upwardly through an opening 51 in side wall 34 and through an internally shouldered bore (not shown) within a cap nut 52 being trapped within a counter bore 53 in the side wall 34. The internally shouldered bore of the cap nut 52 serves as a bearing for the adjustment screw 50. Thus, it will be observed that said U-shaped support frame 43 is suspended within the chamber 42 by the bar 47 and the adjustment screw 50. Therefore, by selective rotation of the adjustment screw 50, the bar 47, and hence the U-shaped support frame 43, may be vertically raised and lowered within the guideways g--g' in chamber 42.

Spacedly upwardly of the web 45 of the frame 43 there is provided aligned aperatures (not shown) for receiving the end portions of a pivot pin 54. Provided surroundingly of the pivot pin 54 in the region between the flanges 44,44, there is a sleeve 55 which is integrally formed within an upwardly extending, relatively thin mounting plate 56 being of slightly less width than the distance between the flanges 44,44. The sleeve remote end of the mounting plate 56 is fabricated with a flange 57 to which is fixed the lower portion of a bubble housing 58 being of cylindrical configuration having a front wall 59, and a rear wall 60 and a peripheral side wall 61 therebetween. The said walls 59, 60 and 61 define with their inner faces an air chamber 62 for purposes to be presently described.

Mounted to the side wall 61 in diametrically opposed relationship with the flange 57 of the mounting plate 56 is a skirt 63 of a flag arm 64 having outwardly diverging side margins 65,65 projecting outwardly and upwardly from said skit 63 and terminating into an end margin 66. Said flag arm 64 is of flat-plate construction having a U-shaped cut-out 67 provided intermediate the side margins 65,65 and opening through the end margin 66. The bar 47 passes through the cut-out 67.

The flag arm 64, the bubble housing 58 and the mounting plate 56 constitute a pendulum bubble unit S, or sensor control means, the operation of which will be described in detail hereinbelow.

The chamber 42 is filled with dampening liquid; such as water, mineral oils, silicones, or any other liquid having suitable viscosity and temperature characteristics to properly dampen the bubble housing 58 in the peculiar ambient conditions, to a predetermined level x (FIG. 2) within which the bubble housing 58 is substantially immersed. In the region of liquid level x the side wall 34 is formed with an internally threaded opening 68 for accommodating a closure plug 69, Accordingly, the liquid level within the chamber 42 may be conveniently controlled and maintained through the opening 68.

Mounted to the inner face 39 of the side wall 34, in the region of the bubble housing 58, are a pair of opposed dampeners 70,70, each of which project radially inwardly and terminate into an arcuate wall 71,71 respectively, being formed on a slightly greater radius than the side wall 61 of the bubble housing 58 to develop a spacing 72,72, respectively, therebetween. Said dampeners 70,70 assure against untoward movement of liquid within the chamber 42 which would adversely affect the operation of the bubble housing 58, and hence the sensor control unit S.

Since the bubble housing 58 is immersed in liquid, it will move responsive to the axial movement or tilting about the vertical axis vv of the pendulum body 31. Therefore, anytime the cutting blade 30 undergoes an angle change relative to the horizontal, the sensor control unit S will swing away from the plane containing the vertical axis vv for purposes to be now described.

Fixed to the exterior side of said interior face 36, in the zone of the recess 32, as by angle brackets 73, are a pair of spaced-apart light source heads 74,74 located on opposite sides of said U-shaped support frame 43, as best seen in FIG. 4. Each light source head 74,74 incorporates a cylindrical body 75,75 projecting through a suitable opening in the interior face 36 for communication within chamber 42. Each light source head 74,74 projects a beam of light b, indicated in phantom lines in FIG. 4, into the chamber 42; the cylindrical body 75,75 being adjustably mounted so that the focal point f of a light beam b is positioned in planar alignment with the vertical axis vv of body 31. Said light source heads 74,74 are in circuit through leads 76,76, respectively, to a convenient source of power, such as a vehicle battery B, for supplying a continuous source of power thereto so that a light beam b is projected at all times during operation.

Mounted on the exterior side of the interior face 36 in the zone of opening 33, as by brackets 77, there are a pair of sensing heads or receivers 78,78 each having a cylindrical body 79,79 positioned within a suitable opening in the interior face 36 in axial alignment with the opposed cylindrical bodies 75,75, respectively, of the light source heads 74,74, respectively. Each of said sensing receivers 78,78 are adapted to receive the light beam b projected by the axially aligned light source heads 77,77, respectively, for closing a circuit; each sensing receiver 78,78 being connected by leads 80,80, respectively, to an amplifier 81 (FIG. 5), one side of which is connected to ground by a lead 82, the other side to the battery B by a lead 83. It will be observed that when the sensor control unit S is in a normal position, the side margins 65,65 of the flag arm 64 block each light beam b for maintaining the sensing receivers 78,78 in a circuit opened position. The flag arm 64 is positioned within chamber 42 so that it is in planar alignment with the focal point f of the light beam b. (FIG. 4).

Depending on which direction the flag arm 64 is swung responsive to the movement of the bubble housing 58 within the fluid chamber 42, one of said side margins 65,65 will swing out of blocking engagement with the related light beam b for permitting transmittal of same to the axially aligned sensing receiver 78 or 78' for closing the circuit. The signals emitted by the sensing receivers 78 or 78 are transmitted to the amplifier 8 1 for enhancing the emitted signal. The amplifier 81 is connected by the leads 84,84 and the leads 85,85 to electric solenoids 86, 87, respectively, which solenoids 86, 87, are positioned on opposed ends of a spool valve 88 incorporated within a master valve M. The master valve M also incorporates a spool valve 88' for operative connection to a position sensing apparatus (not shown) and the ram 24 for effecting the raising and lowering of same, as previously described in my copending application Ser. No. 160,741, filed July 8, 1971, and therefore will not be described.

Said spool valve 88 is in communication with the hydraulic ram 24 by conduits 89, 90 which are connected to ports 91, 92, respectively, located adjacent the opposed end portions of said hydraulic ram 24. Additionally, the master valve M is connected by a conduit 93 to the discharge side of a pump P, the intake side of which is connected by a conduit 94 to a reservoir 95 of hydraulic fluid, said reservoir 95 also being connected to the master valve M by a return line 96. Therefore, by selective energization of solenoids 86 and 87 through the signals emitted by the sensing receivers 78 or 78' respectively, the hydraulic ram 24 will effect a raising and lowering of said cutting blade 30 in accordance with slope requirements.

In operation, with the cutting blade 30 being presented at its desired cutting angle through manipulation of the hand crank C, the flag arm 64 is vertically adjusted through the adjustment screw 50 to the desired position in accordance with the design tolerances. Ifthe angle of the cutting blade 30 is increased, as in a situation when the opposite end portion of the cutting blade 30 lowers, the flag arm 64 will be moved out of blocking relationship with the sensing receiver 78 for closing a circuit thereto through leads 84,84 to the solenoid 86 for energizing same which establishes communication between the conduits 93 and 89 for supplying hydraulic fluid from reservoir 95 to the hydraulic ram 24. Upon entering the hydraulic ram 24 through the port 91, the fluid will push piston downwardly for lowering the cutting blade until the flag arm 64 again blocks the light beam b. The fluid within the hydraulic ram 24 on the downward side of piston 25 will pass through the port 92 for return through conduit 90, master valve M, and return line 96 to the reservoir 95. Similarly, when the flag arm 64 is swung in the other direction, upon the decrease of the cutting blade angle through the raising of the opposite end portion of the cutting blade 30, the circuit is completed to the sensor receiver 78' for emitting a signal through the leads 85,85 for energizing the solenoid 87 wherein fluid from the reservoir 95 will be pumped through conduits 93 and 90 for raising the piston 25 and hence the cutting blade 30. The fluid within the hydraulic ram 24 on its upward side will be returned through conduits 89, master valve M and the return line 96 to the reservoir 95. Thus, it will be observed that as the flag arm 64 swings within the chamber 42 through the movement of bubble housing 58, the circuits will be opened and closed through the sensing receivers 78,78 for alternatively energizing the solenoids 86, 87 respectively, which selectively control the supply of fluid to the hydraulic ram 24 to energize the piston 25 for elevating and lowering the cutting blade 30 and thereby maintain the proper cutting angle of the cutting blade 30.

Through the adjustment screw 50, the flag arm 64 may be adjusted vertically within chamber 42 so that the side margins 65,65 may be positioned at the focal point f of both light beams b. With the flag arm 64 so centered accuracy to 0.005 inch of the flag arm 64 may result in an adjustment of the cutting angle of the blade 30. Since the work accomplished by the flag arm 64 passing through light beam b is a relatively frictionless operation, the pendulum light sensor A offers a more reliable sensing instrument than heretofore thought possible. Additionally, the accuracy of the flag arm 64 may be increased or decreased depending on job conditions by merely turning the adjustment screw 50 so as to move the margins 65 and 65' either closer to the focal point f or further away.

Having thus described our invention, what we claim and desire to obtain by Letters Patent is:

1. A pendulum sensing apparatus comprising:

A body;

Means defining a chamber in said body, said chamber containing a dampening fluid;

Sensor means including:

Light projecting means mounted to said body for transmitting beams of light within said chamber; and

A pair of parallel, spaced-apart sensing receivers mounted within said body and adapted to receive said beams of light for energizing same;

A pendulum member having end portions, presented within said chamber;

Support means slideably mounted within said body;

Means pivotally mounting one end portion of said pendulum member to said support means, the other end portion of said pendulum member being free;

Said pendulum member having a bubble housing located between said end portions, said bubble housing being floatatable within said dampening fluid and being sensitive to the shifting movement thereof;

The free end portion of said pendulum member constituting a flag arm carried by said bubble housing, said flag arm having side margins projecting divergingly outwardly from said bubble housing so that the width of said flag arm increases as the distance from said bubble housing increases;

Said flag arm being normally presented between said light projecting means and said sensing receivers for interrupting said beams of light to maintain said sensing receivers in circuit-opened condition, the width of said flag arm in the region adjacent said bubble housing being greater than the distance between the centers of said sensing receivers;

Adjustment means connected to said support means for moving said support means relative to said body to alter the relative position between the width of said flag arm and the plane containing the centers of said sensor means.

2. A pendulum sensing apparatus as defined in claim 1 and further characterized by:

Said support means comprising a frame;

Means defining guideways formed within said body;

Said frame having a pair of spaced-apart flanges slideably received within said guideways, and a web connecting said flanges;

Said adjustment means operatively connected to said support frame.

3. A pendulum member as defined in claim 2 and further characterized by:

Said body having first and second parallel spacedapart walls and an intervening side wall, said walls constituting said means for defining a chamber;

Said guideways being formed within said first and second walls;

A pair of opposed dampener members mounted to said side wall in the region of said bubble housing, each dampener member extending inwardly of said chamber having an arcuate end wall positioned spacedly from said bubble housing.

4. A pendulum sensing apparatus as defined in claim 2 and further characterized by:

Said support flanges having slots formed in the webremote end portion thereof;

Said adjustment means comprising a cross bar having end portions received within said slots;

An adjustment member operatively connected to said cross member and projecting outwardly of said body.

5. A pendulum sensing apparatus as defined in claim 4 and further characterized by:

Said flag arm having a cut-out interposed between said side margins;

Said cross member extending through said cut-out for limiting the extent of swingable movement of said pendulum member.

6. A pendulum sensing apparatus as defined in claim 4 and further characterized by:

Said cross member having a tapped opening;

Said adjustment member comprising an adjustment screw having a threaded portion engaged within said tapped opening.

7. An apparatus for maintaining a cutting implement at a predetermined attitude relative to a work surface comprising in combination:

A body carried by said cutting implement;

Means defining a chamber within said body;

Fluid means received within said chamber;

A pendulum arm swingably mounted within said chamber;

lncapsulated bubble means, carried by said pendulum arm and immersed within said fluid means, for swinging said pendulum arm upon shifting movement of said fluid means responsive to a change in attitude of said cutting implement;

Elevator means operatively connected to one end portion of said cutting implement for raising and lowering same to maintain the predetermined attitude;

Light projecting means for transmitting beams of light within said chamber;

Sensor means including a pair of light sensing receivers adapted for energization upon receiving a beam of light, said light sensing receivers being located within said body having centers in axial alignment with said beams of light;

Means operatively connecting said light sensing receivers and said elevator means for effecting actuation of said elevator means responsive to the encrgization of said sensing receivers;

Sensor control means for effecting energization of said sensing receivers responsive to the swingable movement of said pendulum arm, said sensor control means comprising a flag arm connected to said incapsulated bubble means and interposed between said light projecting means and said sensor means for blocking said beams of light to maintain said light sensing receivers in deenergized condition;

Said flag arm having side margins projecting divergingly outwardly from said incapsulated bubble means, the distance between said side margins in the region adjacent said incapsulated bubble means being greater than the distance between the centers of said light sensing receivers;

Means for moving said flag arm in a plane normal to the plane containing the centers of said light sensing receivers to adjust the sensitivity of said sensor control means. I

8. An apparatus as defined in claim 7 and further characterized by:

Said means for moving said flag arm including:

A support frame having a pair of parallel flanges carrying said pendulum arm;

Means defining guideways within said body for receiving the flanges of said support frame; and

Adjustment means operatively connected to said support frame for slideably moving same within said guideways.

9. An apparatus as defined in claim 8 and further characterized by:

Said adjustment means comprising:

A cross member having end portions supporting said support frame; and,

An adjustment member operatively connected to said cross member and projecting outwardly of said body.

10. An apparatus as defined in claim 9 and further characterized by:

Said flared end portion having a cut-out interposed between said diverging margins;

Said cross member extending through said cut-out for limiting the extent of swingable movement of said pendulum arm.

11. A surface finishing vehicle of the type used for moving earth comprising:

A mobile frame adapted for travel over ground;

A cutting blade adjustably supported from said mobile frame and preset at a predetermined angle relative to the ground;

An elevator mechanism operatively connected to one end portion of said cutting blade for adjusting the angle of same;

A pendulum sensor apparatus comprising a body centrally mounted on said cutting blade;

Means defining a chamber within said body;

A dampening fluid received within said chamber;

A pendulum member rockably mounted within said chamber and including a sensor control arm and an incapsulated bubble;

Said incapsulated bubble being immersed in said dampening fluid and adapted to swing said pendulum member upon shifting movement of said dampening fluid in accordance with a change in attitude of said cutting blade;

Sensor means within said chamber comprising first and second light sensing receivers arranged in parallel, spaced-apart relationship;

Light projecting means within said chamber disposed in opposed, registering relationship with said first and second light sensing receivers;

Means operatively connecting said sensor means to said elevator mechanism for selectively raising and lowering said one end portion of the cutting blade to maintain same at the desired attitude;

Said sensor control arm having an end portion positioned for normally interrupting said light projecting means to maintain said sensor means in circuitopened condition, said sensor control arm being adapted for energizing said sensor means responsive to the rockable movement of said pendulum member;

Said sensor control arm end portion being flared having outwardly diverging margins, the distance between said diverging margins being greater than the distance between the centers of said light sensing receivers; i

Means for longitudinally moving said pendulum member to selectively adjust the distance between said diverging margins relative to the plane containing the centers of said first and second light sensitive receivers.

12. A surface finishing vehicle as defined in claim 11 and further characterized by:

Said means for longitudinally moving said pendulum member including:

A support frame having side members carrying said pendulum member for rockable movement therebetween;

Means defining guideways within said body for accommodating said side members;

A transverse member having end portions supporting the related side member of said support frame; and

Adjustment means operatively connected to said transverse member for slideab ly moving said side members within said guideways.

13. A surface finishing machine as defined in claim 12 and further characterized by:

Said sensor control arm having a. cut-out located between said diverging margins;

Said transverse member passing through said cut-out for restricting the rockable movement of said pendulum member. 

1. A pendulum sensing apparatus comprising: A body; Means defining a chamber in said body, said chamber containing a dampening fluid; Sensor means including: Light projecting means mounted to said body for transmitting beams of light within said chamber; and A pair of parallel, spaced-apart sensing receivers mounted within said body and adapted to receive said beams of light for energizing same; A pendulum member having end portions presented within said chamber; Support means slideably mounted within said body; Means pivotally mounting one end portion of said pendulum member to said support means, the other end portion of said pendulum member being free; Said pendulum member having a bubble housing located between said end portions, said bubble housing being floatatable within said dampening fluid and being sensitive to the shifting movement thereof; The free end portion of said pendulum member constituting a flag arm carried by said bubble housing, said flag arm having side margins projecting divergingly outwardly from said bubble housing so that the width of said flag arm increases as the distance from said bubble housing increases; Said flag arm being normally presented between said light projecting means and said sensing receivers for interrupting said beams of light to maintain said sensing receivers in circuit-opened condition, the width of said flag arm in the region adjacent said bubble housing being greater than the distance between the centers of said sensing receivers; Adjustment means connected to said support means for moving said support means relative to said body to alter the relative position between the width of said flag arm and the plane containing the centers of said sensor means.
 2. A pendulum sensing apparatus as defined in claim 1 and further characterized by: Said support means comprising a frame; Means defining guideways formed within said body; Said frame having a pair of spaced-apart flanges slideably received within said guideways, and a web connecting said flanges; Said adjustment means operatively connected to said support frame.
 3. A pendulum member as defined in claim 2 and further characterized by: Said body having first and second parallel spaced-apart walls and an intervening side wall, said walls constituting said means for defining a chamber; Said guideways being formed within said first and second walls; A pair of opposed dampener members mounted to said side wall in the region of said bubble housing, each dampener member extending inwardly of said chamber having an arcuate end wall positioned spacedly from said bubble housing.
 4. A pendulum sensing apparatus as defined in claim 2 aNd further characterized by: Said support flanges having slots formed in the web-remote end portion thereof; Said adjustment means comprising a cross bar having end portions received within said slots; An adjustment member operatively connected to said cross member and projecting outwardly of said body.
 5. A pendulum sensing apparatus as defined in claim 4 and further characterized by: Said flag arm having a cut-out interposed between said side margins; Said cross member extending through said cut-out for limiting the extent of swingable movement of said pendulum member.
 6. A pendulum sensing apparatus as defined in claim 4 and further characterized by: Said cross member having a tapped opening; Said adjustment member comprising an adjustment screw having a threaded portion engaged within said tapped opening.
 7. An apparatus for maintaining a cutting implement at a predetermined attitude relative to a work surface comprising in combination: A body carried by said cutting implement; Means defining a chamber within said body; Fluid means received within said chamber; A pendulum arm swingably mounted within said chamber; Incapsulated bubble means, carried by said pendulum arm and immersed within said fluid means, for swinging said pendulum arm upon shifting movement of said fluid means responsive to a change in attitude of said cutting implement; Elevator means operatively connected to one end portion of said cutting implement for raising and lowering same to maintain the predetermined attitude; Light projecting means for transmitting beams of light within said chamber; Sensor means including a pair of light sensing receivers adapted for energization upon receiving a beam of light, said light sensing receivers being located within said body having centers in axial alignment with said beams of light; Means operatively connecting said light sensing receivers and said elevator means for effecting actuation of said elevator means responsive to the energization of said sensing receivers; Sensor control means for effecting energization of said sensing receivers responsive to the swingable movement of said pendulum arm, said sensor control means comprising a flag arm connected to said incapsulated bubble means and interposed between said light projecting means and said sensor means for blocking said beams of light to maintain said light sensing receivers in deenergized condition; Said flag arm having side margins projecting divergingly outwardly from said incapsulated bubble means, the distance between said side margins in the region adjacent said incapsulated bubble means being greater than the distance between the centers of said light sensing receivers; Means for moving said flag arm in a plane normal to the plane containing the centers of said light sensing receivers to adjust the sensitivity of said sensor control means.
 8. An apparatus as defined in claim 7 and further characterized by: Said means for moving said flag arm including: A support frame having a pair of parallel flanges carrying said pendulum arm; Means defining guideways within said body for receiving the flanges of said support frame; and Adjustment means operatively connected to said support frame for slideably moving same within said guideways.
 9. An apparatus as defined in claim 8 and further characterized by: Said adjustment means comprising: A cross member having end portions supporting said support frame; and, An adjustment member operatively connected to said cross member and projecting outwardly of said body.
 10. An apparatus as defined in claim 9 and further characterized by: Said flared end portion having a cut-out interposed between said diverging margins; Said cross member extending through said cut-out for limiting the extent of swingable movement of said pendulum arm.
 11. A surface finishing vehIcle of the type used for moving earth comprising: A mobile frame adapted for travel over ground; A cutting blade adjustably supported from said mobile frame and preset at a predetermined angle relative to the ground; An elevator mechanism operatively connected to one end portion of said cutting blade for adjusting the angle of same; A pendulum sensor apparatus comprising a body centrally mounted on said cutting blade; Means defining a chamber within said body; A dampening fluid received within said chamber; A pendulum member rockably mounted within said chamber and including a sensor control arm and an incapsulated bubble; Said incapsulated bubble being immersed in said dampening fluid and adapted to swing said pendulum member upon shifting movement of said dampening fluid in accordance with a change in attitude of said cutting blade; Sensor means within said chamber comprising first and second light sensing receivers arranged in parallel, spaced-apart relationship; Light projecting means within said chamber disposed in opposed, registering relationship with said first and second light sensing receivers; Means operatively connecting said sensor means to said elevator mechanism for selectively raising and lowering said one end portion of the cutting blade to maintain same at the desired attitude; Said sensor control arm having an end portion positioned for normally interrupting said light projecting means to maintain said sensor means in circuit-opened condition, said sensor control arm being adapted for energizing said sensor means responsive to the rockable movement of said pendulum member; Said sensor control arm end portion being flared having outwardly diverging margins, the distance between said diverging margins being greater than the distance between the centers of said light sensing receivers; Means for longitudinally moving said pendulum member to selectively adjust the distance between said diverging margins relative to the plane containing the centers of said first and second light sensitive receivers.
 12. A surface finishing vehicle as defined in claim 11 and further characterized by: Said means for longitudinally moving said pendulum member including: A support frame having side members carrying said pendulum member for rockable movement therebetween; Means defining guideways within said body for accommodating said side members; A transverse member having end portions supporting the related side member of said support frame; and Adjustment means operatively connected to said transverse member for slideably moving said side members within said guideways.
 13. A surface finishing machine as defined in claim 12 and further characterized by: Said sensor control arm having a cut-out located between said diverging margins; Said transverse member passing through said cut-out for restricting the rockable movement of said pendulum member. 